A liquid crystal projector generally utilizes a liquid crystal display (LCD) panel in which modulation is controlled according to an applied voltage to display an image on a screen. Liquid crystal projectors have been utilized with one, two and three LCD panels.
Color field sequential projection systems using a single reflective display panel have two primary limitations: lower lumen output because only one color band of light is projected at any given time; and, color splitting artifacts that occur during times when the viewer's eye is shifting to different parts of the displayed image or while the viewer's eye is tracking motion in the display.
Brightness has been increased by adding a second display device to the system to display one color, typically red, which is always on and by sequencing the remaining two colors, typically blue and green. This two-panel system increases the brightness by approximately fifty percent and provides more red light on the screen for color balancing when red deficient lamps are used in the illumination system. The addition of a second color on the screen also helps the color splitting artifacts due to the eye's less sensitive response to the secondary color combinations, such as yellows, magentas and cyans, rather than the saturated primary colors, i.e., reds, greens and blues.
Color splitting artifacts have been reduced by increasing the number of color fields projected during a single frame. For example, projecting six fields (red, green, blue, red, green, and blue) in a single frame rather than just three fields, causes the artifacts to be smaller and therefor less noticeable. However, most reflective LCD devices are not fast enough to increase the number of fields to six per frame so this technique is not possible for slower devices, i.e., devices only capable if projecting five or less fields per frame.
In another two-panel embodiment, such as described in U.S. Pat. Nos. 5,863,125 and 5,921,650, two-panels are utilized with a colorwheel that sequences different color band polarizations to a polarized light beam splitter (PBS) cube that sends a particular waveband to one or the other panel. However, the brightness of the device is limited because the device does not send two different wavebands simultaneously to each of the LCD panels but instead uses one LCD panel at a time to allow for “dead time” of the other LCD panel. Thus, each LCD displays a separate sequence of red, green and blue (RGB) images, but only one color image is present on the screen at any given time.
In yet another two-panel embodiment, such as described in U.S. Pat. No. 5,629,743, two-panels are utilized to provide a luminance signal and a color signal, wherein a processor uses the signals to conduct mathematical manipulation to produce a second luminance signal and a second color signal. Accordingly, the system is complicated and does not provide a good method of physically implementing a projector for reflective display devices.
Systems utilizing three LCD panels include a single panel for each color component. Thus, the brightness of the image is slightly increased. However, due to the higher number of components, the structure is complicated and expensive to manufacture and maintain.